Percolation Behaviour in the Magnetic Permeability and Electrical Conductivity in Conducting Magnetic - Insulating Non Magnetic Binary Composites

Abstract

Experimental results of the complex magnetic permeability (μ) and the electrical conductivity (σ) of a granular paramagnetic Gadolinium Gallium Garnet (GGG: 0.3 to 26 Vol. %) and Teflon (PTFE) system are presented, and discussed in relation to previously published (conductivity) and unpublished (permeability) studies on granular Fe₃O₄ - talc and Ni - talc wax systems. In these systems, plots of the real conductivity ( ${\sigma }_{\text{m}}^{\text{'}}$ ) against the volume fraction (φ) lie on a characteristic sigmoid curves that when fitted to the Two Exponent Phenomenological Percolation Equation (TEPPE), confirm the existence of "percolation microstructures" with critical volume fractions (φ _c). The plots of the real and imaginary permeability ( ${\mu }_{\text{m}}^{\text{'}}$ ) and ( ${\mu }_{\text{m}}^{″}$ ), satisfactorily fit to the TEPPE using the φ _c obtained in each case from the "conductivity" measurements. In all three cases, the conductivity results gave the exponent t > 2, and the permeability results gave t < 1.